The use of radon-free building materials
A very small percentage of houses in the U.S. have elevated indoor radon levels due to the building materials. In most of these cases, the problems arose through the use of known radioactive wastes, such as uranium mine tailings, for the aggregate in concrete blocks or as backfill around houses. In the other cases, the radon came from the extensive use of uranium-bearing rocks in fireplaces and other interior decorative applications. Such rocks include some light-colored (felsic) volcanics, granite, phosphorite and phosphatic limestone, and the metamorphic rocks derived from these materials. In general, stone building materials are not a significant source of indoor radon.